I'd avoid that like a dose of aids, Decent quality HF Linears tend to be quite expensive, Take a look round some of the amateur radio retailers websites, You might find a used one at a reasonable price.

I suspected that it might be a waste of cash. Rather than paying big bucks for an amp i might be better selling the radio on, adding a bit of dosh and getting something with better power output and maybe even a built-in tuner. Something like a 450D?

Depends what you are aiming to do with it ! I've got a 450d and used it mobile quite a lot but it became a right royal PITA putting it in the car etc, so I found an IC 703 and put that in as a permanent install with a little extra help for 11m SSB, I keep bidding on 706's & 857's but the latter are still holding strong money, the 450 now sits on the desk at home unused due to s9 of noise.